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Understanding Smoke and Carbon Monoxide Detectors

This Old House master electrician Heath Eastman teaches host Kevin O’Connor everything he needs to know about these fire safety devices.

Master electrician Heath Eastman shows Kevin O’Connor everything he needs to know about smoke and carbon monoxide detectors. The two discuss the different types of smoke detectors available and how they operate and interconnect. Then, Heath shows Kevin the difference between a smoke detector and a carbon monoxide detector, highlighting the importance of having both in a home.

Two Types of Smoke Detectors

There are two types of smoke detectors: ionization and photoelectric. These devices will activate in the presence of smoke, but they both specialize in a particular type of combustion. Photoelectric detectors will detect smoldering fires sooner than ionization detectors, whereas ionization detectors will react sooner to flames.

Each box (and the back of each device) will indicate which type of detector it is.

Location Matters

When choosing a smoke detector, the area in the home makes a difference. For example, a steamy shower can set off an ionization detector in the hallway outside the bathroom. A photoelectric detector is a better choice for that area. The same would apply to kitchens or anywhere moisture may be present. However, mixing and matching photoelectric and ionization detectors throughout the home is fine.

Ask the AHJ

The AHJ (Authority Having Jurisdiction) is the best source for information about how many smoke detectors are necessary and where to put them. In most cities, the AHJ is the fire department, but the building department might also oversee these regulations.

Manufacturer Date

It’s important to know how old a smoke detector is, so manufacturers label the back of each device with a manufacture date. Detectors older than 10 years should be replaced, regardless of whether they still appear to be working.

Battery vs. Hardwired

Battery-operated smoke detectors are easy to install and can go anywhere the homeowner needs one. However, these devices typically alert individually, which means an activation for one device will not trigger the others.

Conversely, many local codes now require hardwired detectors. These detectors plug into the home’s fire alarm system, providing constant power while still having a battery backup. When these devices alert, they will typically activate all of the smoke detectors in the home. However, each device needs an alarm wire run to the device’s location, making these models much more difficult to install.

Carbon Monoxide Detectors are Just as Important

Carbon monoxide is odorless and tasteless, meaning that a carbon monoxide detector may be the only way to know there’s an issue. Carbon monoxide detectors come in several plug-in, battery-operated, and hardwired varieties. They even come in combination units, featuring both carbon monoxide and smoke detection from one device.

Combination models will give voice alerts to explain whether the issue is smoke or carbon monoxide-related.

Detector Location Best Practices

Always check with the AHJ, but there are some general rules and best practices when choosing detector locations:

  • Place smoke detectors in the bedrooms
  • Install a smoke and carbon monoxide detector just outside of the bedrooms in the hallway
  • Install a smoke and carbon monoxide on every level, including the basement, first floor, second floor, and attic

Garages are Different

A smoke detector or carbon monoxide detector in the garage can cause accidental activation. Instead, place a heat detector in the garage. These detectors alert when a garage space heats too quickly or when they reach a certain temperature. Heat detectors can also be hardwired into the home’s fire alarm system.

10-Year Batteries

Many folks remove the batteries inside the smoke detectors to prevent nuisance alarms, leaving the home unprotected. To combat this, manufacturers now sell detector units with sealed batteries that last 10 years (the same as the sensors in the device). Once the device reaches 10 years, it alerts that it’s near the end of life, and the user can replace it instead of just the batteries.

Smart Devices Exist, Too

While smart smoke and carbon monoxide detectors do communicate with each other to activate the entire system in alarm, they aren’t universally accepted yet. Smart devices use the home’s WiFi to alert a smart hub or the homeowner’s smartphone. These devices come in both battery and hardwired configurations and smoke and carbon monoxide combinations. This makes the AHJ the best resource for determining whether they’re allowed or not.